As conventional processes for producing an electrically conductive film which can shield electromagnetic waves while maintaining satisfactory light transparency there are known, for example, a process in which a transparent, electrically conductive film such as, for example, indium-tin oxide film (ITO film) is formed as a thin film on the surface of a transparent glass or plastic substrate by vapor deposition or sputtering or a process in which a thin metal film is formed throughout the whole surface of a transparent glass or plastic substrate by metal plating or vapor deposition and is then processed for example by photolithography to form a fine mesh of the thin metal film.
The above transparent, electrically conductive film having ITO film on a transparent substrate is superior in light transparency, but is inferior in electrical conductivity and cannot afford satisfactory electromagnetic wave shielding properties in comparison with the transparent, electrically conductive film having a mesh-like thin metal film. On the other hand, in the process involving forming a thin metal film on a transparent substrate and processing it into mesh-like, since most of the thin metal film is removed, this is wasteful and results in an increase of the production cost, although there is attained high electrical conductivity.
In an effort to solve the above-mentioned problems, for example in JP 62-57297A and JP 2-52499A there is proposed a process wherein electrically conductive ink or ink containing an electroless plating catalyst is printed in the shape of a pattern consisting of thin lines onto a base material such as a transparent film or glass and thereafter metal is plated onto the ink layer. According to this process, however, it is difficult to prepare a pattern using thin lines not larger than 30 μm in line width, and a large line width results in deterioration of light transparency; besides, when the transparent, electrically conductive film formed by this process is used as an electromagnetic wave shielding material for display, it is inferior in image visibility.
Further, when the transparent, electrically conductive film is used as an electromagnetic wave shielding material for PDP, it is laminated to, for example, an infrared absorbing film with use of an adhesive. In this case, in the transparent, electrically conductive film formed by the above process, the ink layer after printing is thick and concaves and convexes on the print surface are large, so when the adhesive is applied to the surface of one film and this film is laminated to the other film, there easily occurs inclusion of air bubbles and image visibility is deteriorated in the presence of such air bubbles.
On the other hand, in JP 2000-137442A there is proposed a process involving laminating a transparent base material and metal foil to each other with use of an adhesive and thereafter making the metal foil mesh-like by photolithography. According to this an adhesive and thereafter making the metal foil mesh-like by photolithography. According to this process, thin lines not larger than 20 μm in line width permits the attainment of high light transparency, but a warp caused by the adhesive is apt to occur. Moreover, as is the case with the process referred to previously, since the metal foil thickness is not smaller than 10 μm, surface concaves and convexes become large and there occurs inclusion of air bubbles upon lamination to another member.